The present invention relates to a magnetron and a microwave oven therewith.
An anode of a typical magnetron used for a microwave oven has an anode cylinder, an even number of vanes and a plurality of strap rings. The even number of vanes are shaped as plate and arranged in the anode cylinder. The even number of vanes are arranged in a radial pattern of which center is at an axis of the anode cylinder. Each of the plurality of vanes connects vanes arranged alternatively around the axis among the even number of vanes to equalize electrical potential.
For example, a structure in which two strap rings are located in the middle of vane in the direction of axis is disclosed in Japanese Examined Patent Application Publication S50-20433. This structure makes it difficult to manufacture the anode and it takes much time to manufacture the anode.
In Japanese Utility Patent Application Publication S61-183054, a structure in which two large/small strap rings 241, 243 are arranged on only one end of vanes in a direction of an axis 22 as shown in FIG. 11 is disclosed. In Japanese Patent Application Publication H05-128976, a structure in which three, small/medium/large strap rings are arranged on only one end of vanes in a direction of the axis is disclosed. Because a plurality of vanes are arranged on only one end, these structures deteriorate balance of electrical potential at one end and the other end and may raise a problem about oscillation stability.
In Japanese Patent Application Publication 2009-81018, a magnetron having four strap rings including two large strap rings 141a, 141b of the same diameter and two small strap rings 143a, 143b of the same diameter as shown in FIG. 12 is disclosed. In this magnetron, two large and small strap rings 141a, 143a is arranged on one end of vanes 130 in the direction of axis 22 and two large and small strap rings 141b, 143b is arranged on the other end of vanes in the direction of axis 22. Therefore, it is easy to manufacture and has good balance of electrical potential and good stability of oscillation.
The magnetron disclosed in Japanese Patent Application Publication 2009-81018 has two large strap rings 141a, 141b of the same diameter and two small strap rings 143a, 143b of the same diameter. These four strap rings are produced as rings by punching a copper sheet as shown in FIG. 13.
To produce four strap rings in total, two copper sheets of which sides are larger than outer diameter of the large strap rings 141a, 141b are required. As described, the magnetron disclosed in Japanese Patent Application Publication 2009-81018 utilizes sheet metal at low efficiency and increases material cost.